1. Field of the Invention
the present invention relates to thermal conversion processes, in particular to pyrolysis of carbonaceous feedstocks, such as biomass and organic wastes. According to the process, the carbonaceous material is fed into a reactor, wherein the feedstock is converted at moderate temperature in the presence of a heat transfer medium comprising particulate matter. The particulate matter is kept in fluidized state by a fluidizing gas. After pyrolysis, the particulate matter is separated from the hydrocarbon products, it is regenerated by combustion and recirculated to the reactor. The products of the pyrolysis comprise solids, liquids and/or gases which are recovered from the reactor. Optionally the products are subjected to further processing steps, for example by condensation of the vaporized hydrocarbons.
2. Description of Related Art
The continuing and increasing concern of society for environmental problems related to fossil fuel use and disposal of waste materials has led to increased research into and development and commercialization of a wide variety of technologies which aim to enhance the collection, processing and use of materials in an environmentally responsible manner.
At present the expanded use of organic based materials from solid waste streams and forestry residues or purpose grown crops is hindered by the relatively high costs in comparison to the existing infrastructure for employing fossil fuel systems. These high costs are due to both higher feedstock costs and higher conversion costs. The higher conversion costs are related to the well known problem of economy of scale, which is caused by the wide distribution of raw materials which leads to high costs for collection and transport. In terms of biomass conversion, the main goal is to increase the energy concentration in the final product so as to minimize costs during use. Liquids are also preferred due to the ease of handling, shipping and storing as well as because of their favorable characteristics of use.
In general terms, pyrolysis is a thermal degradation process in which large molecules are broken or cracked into smaller molecules. It can be used to convert a variety of solid or liquid materials into a more readily useable form, and it has, in fact, been employed for the production of charcoal and high viscosity tars from biomass for centuries. The process can be described as a thermal cracking or a depolymerization process in the absence or near absence of oxygen. During the past 10-20 years, the technology has been modified to maximize liquid yields by increasing the heating rate to over 1000xc2x0 C./second, reducing the vapour residence time to under 15 seconds and improving the product recovery with a fast quench.
Depending on the feedstock, conventional pyrolysis equipment comprises a drier for the raw material, optionally a mechanical grinder for size reduction, a feed system, a reactor, cyclones for solids removal from the vapour stream, char combustor to provide heat for the reaction and pots for solids removal and recovery system. In addition, a char combustor for process heat is often included. The reactors operate at a slight overpressure.
The above-described process equipment is used for thermal conversion known as xe2x80x9cflashxe2x80x9d or xe2x80x9cfastxe2x80x9d pyrolysis. When applied to small biomass particles ( less than 5 mm thick) and temperatures of 400 to 700xc2x0 C., liquid yields are as high as 65 to 75 wt-%. The other products of the process are char (10 to 15 wt-%) and non-condensable gases such as methane CH4, carbon monoxide CO and carbon dioxide CO2 (10 to 15 wt-%).
The ratio of solids to liquids to gases is determined by both the heating rate and maximum temperature and generally it depends on the specific feedstock. If liquid products are to be maximised it is generally known in the art that intermediate temperatures in the range of 400 to 600xc2x0 C. and relatively short residence times from 0.5 to 5 seconds are most advantageous. These process conditions lead to high yields, on the order of 65 to 75 weight % of the feedstock.
In the art, heat for the endothermic pyrolysis reaction is produced in a separate boiler or regenerator by combusting the uncondensable gases, tar and combustible solids produced in the process. Heat is transferred from the boiler to the reactor by solid particles, e.g. sand. After the chemical reaction the solids may be covered by tar which is combusted in the boiler. Solids (combustible and sand) are generally removed from the gas stream by one or more cyclones, which are placed following the reactor.
Processes for pyrolysis of carbonaceous materials and equipments used in the processes are discussed in the following patents:
W. M. Hearon et. al, xe2x80x9cPreparation of Unsaturated Hydrocarbons from Oxygen Containing Organic Materialsxe2x80x9d U.S. Pat. No. 3,148,227 Issued Sep. 8, 1964
C. K. Choi, xe2x80x9cProcess and Apparatus for Rapid Pyrolysis of Carbonaceous Materialsxe2x80x9d U.S. Pat. No. 4,101,412 issued Jul. 18, 1978
E. L. Capener, M. Low, xe2x80x9cMethod and Apparatus for converting Solid Organic Material to Fuel Oil and Gasxe2x80x9d U.S. Pat. No. 4,344,770 issued Aug. 17, 1982
E. Chornet, C. Roy, xe2x80x9cOrganic Products and Liquid fuels from Lignocellulosic Materials by Vacuum Pyrolysisxe2x80x9d Canadian Patent No. 1,163,595 issued Mar. 13, 1984
D. S, Scott xe2x80x9cPyrolysis Process for Biomassxe2x80x9d Canadian Patent No. 1,241,541 issued Jun. 6, 1988
D. A, Berg, xe2x80x9cMethod and Apparatus for Rapid Thermal Processingxe2x80x9d Canada Patent No. 1,283,880 issued May 5, 1991
The present technology is hampered by some significant problems. Thus, in order to achieve high product quality it is necessary to remove as high percentage of solids from the gases as possible prior to condensation. Solids remaining in the liquid product significantly reduce product quality by clogging small passages in pumps, fuel lines and nozzles and are also suspected to lead to increased polymerization and subsequent increase in viscosity of the liquid fuel.
In the above-mentioned related art, the conventional cyclones and separate reactors and regenerators used have serious limitations restricting their utilization in biomass pyrolysis processes. Thus, the solids are subjected to high velocities in traditional cyclones, which leads to high attrition of both solids and construction materials. The required equipment is large and heavy. Outer surfaces are large, which causes large radiation losses. Vertical distances for solids transport are long, which requires expensive process control equipment.
It is an object of the present invention to eliminate the problems of the prior art and to provide a novel process for pyrolysis of biomass, organic wastes and similar carbonaceous feedstocks.
It is another object of the present invention to provide a novel apparatus for pyrolysis of the afore-mentioned materials.
These and other objects, together with the advantages thereof over known processes, which shall become apparent from specification which follows, are accomplished by the invention as hereinafter described and claimed.
The present invention is based on using a reaction system utilizing at least two internally concentrically arranged cylindrical chemical or physical conversion circulating fluidized bed reactors or thermal regenerators comprising multi-inlet cyclones which permits thermal conversion or pyrolyzation of carbonizable material into a number of liquid, solid and gaseous products.
In particular, the process according to the present invention comprises pyrolysing biomass or organic wastes at temperatures in excess of 400xc2x0 C. in an apparatus including a reactor with a riser having an axially annular cross section and being equipped with a multi-inlet cyclone for the separation of particulate matter, and a regenerator with a riser having an axially annular cross section and being concentrically fitted in respect of the reactor used, said regenerator also being equipped with a multi-inlet cyclone for separation of regenerated particulate matter. According to the invention, the dipleg of the regenerator communicates with the riser of the reaction unit and with the drying unit.
More specifically, the process according to the present invention comprises (a) feeding the feedstock(s) into a fluidized-bed reactor, wherein the feedstock is converted to hydrocarbon products at an elevated temperature under the influence of particulate matter kept in a fluidized state by a fluidizing gas, (b) transferring the particulate matter from the reactor to a regenerator for regeneration and then recirculating the particulate matter to the reactor after the regeneration, and (c) recovering the converted hydrocarbon products from the reactor, wherein said reactor comprises a riser having an axially annular cross section and is equipped with a multi-inlet cyclone for the separation of particulate matter, and wherein said regenerator is concentrically fitted around said reactor and wherein said regenerator comprises a riser having an axially annular cross section and wherein said regenerator is equipped with a multi-inlet cyclone for separation of regenerated particulate matter.
The apparatus according to the invention is as is described hereinabove for practicing the method according to the invention. The present invention achieves considerable advantages. Thus, the traditional problem of high solids content in liquid products has been minimized and it is possible to produce pyrolysis oil, the quality of which is higher than that of oil produced with the processes of the prior art. The incorporation of multi-inlet cyclones into the reactor configuration reduces gas velocities, reduces the physical size of the cyclone and shortens the residence time of gases in the cyclone. This directly leads to a reduction in the outer wall area of the hot reactors, which as a consequence leads to less material required and thus a less expensive reactor. Further, lower gas velocities cut down attrition of construction materials.
Next, the invention will be described in more detail by making reference to the appended drawings.